A Nonlinear Model Based Slip Controller for Heavy Commercial Vehicles

 

The brake system is one of the most critical components of a motor vehicle which ensure its safe operation. The primary function of the brake system is to decelerate the vehicle and stop it when necessary in a stable manner. Most heavy commercial vehicles in India, which include trucks and buses, use the air brake system with S-cam foundation brakes. An Antilock Braking System (ABS) is an additional safety device that is fitted on a vehicle to ensure safety by maintaining stability and steerability of the vehicle during braking in emergency conditions and poor road conditions. Under such adverse conditions, one or more wheels of the vehicle may get locked, which may result in the loss of vehicle stability or steerability or both. An ABS prevents the wheels from locking while braking by modulating the flow of compressed air to the brake chambers under impending locking conditions.

 

The actual control algorithms of ABS devices marketed by manufacturers are not completely known and are proprietary items. The control strategies of commercially available ABS may be based on look up tables, calibrated through extensive experiments and tests, and the system dynamics may or may not have been effectively incorporated in the controller design.

 

The focus of this research is the development of a mathematical model based longitudinal slip control scheme to prevent locking of wheels in commercial vehicles. The development of the slip controller is based on the mathematical model for the longitudinal dynamics of the vehicle during braking and since this model is nonlinear, the control scheme is developed using Lyapunov analysis. The output of the controller is then implemented in an experimental setup to study its physical performance. Such a model based analysis of the brake system of a heavy commercial vehicle will provide better insight into its performance and open room for improvements. This will also allow for computer based analysis which may result in reduction of expensive and time consuming experimental development trial runs. The present study will hopefully contribute towards the indigenous development of ABS for commercial vehicles in India.